Human infertility is one of the most common health problems worldwide and is most frequently linked to aberrant development of male and/or female germ cells. Yet, ethicallly, it is impossible to study early germ cell development (GCD) in vivo in humans. Thus, frequently, results from model organisms are relied upon to understand how germ cells develop. Yet, GCD clearly differs between species. The hypothesis of this proposal is that the hESC system is suitable for genetic studies of human GCD and that GCD can be tracked by assays such as bisulfite genomic sequencing to detect erasure and establishment of imprints in germ cells. Furthermore, it is hypothesized that members of the NANOS gene family are required for human germ cell formation and development. My specific aims are: 1) Characterize differentiation of hESC-derived germ cells in vitro. 2) Characterize genetic dependency of human GCD in vitro by evaluating the roles of NANOS1, 2, and 3 via gene silencing and assaying germ cell formation and development in vitro and in vivo. It is expected that successful completion of these aims will greatly increase our understanding of the mechanisms that underlie a remarkable process: formation and differentiation of human germ cells.